Residual oil recovery process using water containing a surfactant



'v1-1 xvii .zu Jail Allg- 10, 1965 J. H. HENDERSON ETAL 3,199,586

RESIDUAL OIL RECOVERY PROCESS USING WATER CONTAINING A SURFACTANT Filed may 51, 1961 INVENTORS JAA/5 fr. HENDERSON JOSEP/7 J. 75465.?

*United States Patent 3.199,586 RESIDUAL OIL RECOVERY PROCESS USING WATER CONTAINING A SURFACTANT James H. Henderson, Gibsonia, and Joseph J. Taber, j Cheswick, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Filed May 31, 1961, Ser` No. 113,725 8 Claims. (Cl. 166-9) This invention relates to a method for the production of oil from underground oil-bearing formations,and more particularly to the secondary recovery of oil from such formations by a water flooding process.

`Usually underground oil reservoirs suitable for commercial production of oil originally possess sucient energy to move oil in the reservoir to wells drilled into the reservoir. The reservoir energy, which may be in the form of a gas cap under an elevated pressure, gas dissolved in the oil, or a water drive, may be adequate to force the oilupwardly through the wells to the surface; although frequently it is necessary to provide pumps to lift the oil from the bottom of the well to the surface. After the production from the reservoir has continued for an extended period, the length of which will depend upon the characteristics of the reservoir, the reservoir may not contain sufficient energy to move oil to the wells at a rate high enou'ghto permit continued profitable operation of the wells. As much as 70% or even more of the oil initially present in the reservoir may remain underground when production by primary recovery is no longer economically feasible and the reservoir is often referred to as depleted.

One secondary method that has been widely used to increase the amount of oil recovered from a depleted reservoir is the Water flooding process in which water is injected into the reservoir at one or more wells to drive voil from the reservoir to adjacent wells through which the oil is lifted to the surface.- Continued injection of water intoI the reservoir frequently results in fingering of the water through 'the oil bank with the consequent production of increasing amounts of water with the oil. Various methods of plugging the most permeable portions of the formation or increasing the viscosity of the water have been suggested to reduce the lingering of the injection water through the reservoir.

Even if fingering of the water injected into the formation is insignicant, substantial amounts of oil are left in the formation when further injection of water in the conventional water ilood process causes no further production of oil. At this stage of the operation the oil remaining in the formation, referred to as theA residual oil, is present in the formation as a discontinuous phase. An article in the Oil and Gas Journal of May 13, 1957, page 98 et seq., based on extensive studies,shows that the amount of residual oil is independent of the flooding rate and cannot be recovered by further increases in the rate of injection of the water in ranges feasible in oil field ooding operations.

This invention resides in a method for increasing the amount of oil recovered in a water flood operation by injecting water containing a surfactant into a formation in a manner to create a linear drive through the formation. The characteristics of the flood water and the pressure of injection of the flood water are controlled whereby the ratio is greater than.5.0 where AP is the pressure drop between the injection and production passages through the forma- Patented Aug. 10, 1965 tion in pounds per square inch, L is the distance in feet between the injection and production passages and 'y is the interfacial tension in dynes per centimeter between the flood waterv and the oil in the formation. Throughout this specification all references to the ratio FIGURE 2 is a diagrammatic view, partially in vertical section, of an injection and a production well provided with overlapping horizontal fractures for a linear flow water flooding operation utilizing this invention.

FIGURE 3 is a diagrammatic view in horizontal section through the oil-bearing formation of an oil eld in which injection wells are connected by vertical fractures and production wells are connected by other vertical fractures for performing a linear water flood operation in accordance with this invention.

We have found that the recovery of residual oil from a formation is dependent on the ratio of AP Lv which must exceed a critical value. By suitable arrangement of flow passages in the oil-bearing formation, a linear flood pattern can be obtained which results in a substantially uniform pressure gradient over the portion of the formation flooded, whereby, upon reduction of the interfacial tension by the addition of a suitable surfactant to the flood water, the critical ratio of can be exceeded throughout the area of the formation that is Hooded without resorting to tlood rates or injection pressures out of the range of feasible economic practices. Referring to FIGURE l in which the percent of residual oil removed from a core of Berea sandstone by water flooding with aqueous solutions is plotted against the ratio it will be noted that substantially none of the residual oil is removed from the core until exceeds about 5.5, the critical value for the Berea sandstone. The minimum ratio of that will allow recovery of a measurable amount of resi dual oil from the formation will vary from one formation 3 to another. in some formations substantially no residua oil is recovered unless exceeds about 8;

ln all of the formations that have been tested the ratio of required for the production of a measurable portion of the residual oil exceeds 5. Below the critical ratio of A? Lv only insignificant amounts of residual oil are removed exceed about in which event 50% or more of the residual oil will be flushed from the majority of oilbearing formations.

Although the critical ratio of depends upon the characteristics of the formation from which oilis to be recovered, it is independent of the fluid to be displaced from the formation or the displacing uid.

Experimental runs were made in Berea sandstone in which residual air was displaced with water, residual air was displaced with aqueous surfactant, residual Soltrol (a mixtureV of hydrocarbons ofnarrow boiling range similar in density and viscosity to. kerosene) was displaced withA water, residual Soltrol was displaced with an aqueous solution of isopropyl alcohol, and residual Soltrol was displaced withI an aqueous surfactant. The runs were..

made by saturating cores of the sandstone with water, ooding them with the fluid to be displaced, and then flooding. with waterl by imbibitionuntil no further oil or other fluid was recovered. before tioodingv with the dis-v placing flud to be tested. Flooding by imbibition is an eifectivemethod of reducing the residuali oil in a core to as low a value as -wil1 remain after flooding water at ratesfeasible in field operations. The cores were hooded with the displacing fluid at very low rates and the rates 4 As shown in FIGURE l, although the critical ratio of is independent of the displaced and displacing fluid, the amount of oil recovered at ratios above the critical depends on the displacing tluid used.A ln FIGURE 1, curve A shows the residual oil recovered when a core containing residual oil (Soltrol) is flooded with a 0.1% aqueous solution of Triton X-lOO, an alkyl polyoxyethylene derivative of phenol sold by Rohm and Haas, and curve B when a similar core is flooded with an aqueous solution con taining 20% isopropyl alcohol. In every instance the critical ratio is approximately 5 :5, but the recovery of residual oil varied widely at higher ratios with the differ ent flooding liquids.

The interfacial tension between the oil and untreated fresh water or brine is too high to allow a between fresh or salt water and a crude oil is. usually in gradually increased. No appreciable residualruid was displacedfrom the Bereasandstone until above,5.5 always produced a marked increase in the residual fluid displaced.

the range of about 25 dynes per centimeter and with the usual spacing of oil wells in a eld the desirable range of of 2O percent be obtained without the use of excessive pressuresor flow rates. interfacial tensions. between Soltrol and fresh or salt water is in the range of 40 to 50 dynes per centimeter.

By incorporating a surfactant in the ood water the interfacial tension between theA ood water' andthe oil can be reduced to a value at which reasonable pressure gradients readily obtained in linear drive field operations, as hereinafter described, will result in removal of residual nil from an oil-bearing formation in. a water flooding operation. The surfactant incorporated in the flood water should reduce the interfacial tension between the flood water and the oil to below 0.5 dyne per centimeter and preferably below 0.2 dyne per centimeter. Certain surfactants and combinations of surfactants with alkali-metal hydroxides or with brine allow the interfacial tension between the oil and the flooding medium tol be reducedto the stillv more desirable range of 0.05 dyne per centimeter orv less.

AmongtheY many surfactants. suitable foruse infthis.

invention are the. nonionic surface active agents whichy are ordinarily polyoxyethylene derivatives. of water"in-` soluble organic compounds. Typical waterl insoluble organic compounds, generallyreferred to as the hydrophobie group of the surfactants, which are` treated with ethylene oxide to form the polyoxyethylene". derivatives, are fatty alcohols, alkyl substituted phenols, fatty acids, rosin acids, and tall oils. Other nonionic. surface active agents are the esters of the hexahydric alcoholsl such as.

sorbitan rnonooleate and monopalrnitate, the polyoxyethylene derivatives of the fatty acid esters of hexahydric alcohols, and 'ethers of hexahydric alcoholsandethylene oxide.

The effect of a number of nonionic surface-active agents on interfacial tension is illustrated in Table I; Atpet93i,

manufactured by Atlas Powderv Company, is sorbitan TABLE i The effect of noniom'c surface-active agents 0n the interfacial tension between various oils' and water interfacial surfactant Surluctant Tension, Concentra- Oil Phase Writer dynes/cm. tion, lliasc Percent Triton X100 0. 3 10.0 W. M. Smith Gil field crude. brine. Pluronic L-4 0. 5 1. 0 Soltrol 5%brine. Pluronlc L-" 0. 5 1. 0 d Do. Atpet 931--- 0. 5 1. 0 2.5% brine.

TABLE u The effect of sodium hydroxide on the interfacial tension between N. Ward Estes crude oil and Triton X-IOO Sodium llydroxide interfacial Concentration, Tension, dynes/ Percent cui.

Anionic surfactants are also suitable for use in the water flooding process of this invention to reduce the interfacial tension between oil and the surfactant-treated l flood water to the desired range. The anionic surfactants are usually alkylaryl sulfonates or fatty alcohol sulfates.v` f Surfactants'such as Solar 25, a mixed nonionic and anionic surfactant manufactured by Swift & Company, can be used to reduce the interfacial tension to the desired range. amide of fatty acids from coconut oil. The major part of the amide has the formula:

The anionic portion is the diethanolamine salt of dodecyl benzene sulfonic acid. in addition, some free amine and glycerin are found in the detergent so that the total composition is:

Percent Diethanolamide 60 Amine sulfonate 26 Free diethanolamine 8 Free glycerin 6 The interfacial tension between hydrocarbon oils and some aqeous solution of mixed nonionics-anionics are set forth in Table 111.

The nonionic detergent in Solar 25is diethanol-Y Y' l 6 TABLE In The effect of anionic or mixed nnionic-nonionic surfaclants on Ille interfacial tension between oil and water 'l 60% solution of sodium dioctyl suliosuccinate in equal parts isopr0 panal and writer.

2 04% solution ol sodium dioctyl sullosuccnate in a light petroleum distillate solvent.

3 Potassium dioctyl suliosuccinatc.

4 Sodium diliexyl suliosuccincte.

A preferred surfactant used in the process of this invention is Triton GR-5. manufactured by Rohm and Haas. interfacial tensions between Soltrol and water containing Triton GR-S of the order of 0.025 dyne per centimeter can be obtained when the surfactant is employed in a brine solution. Triton GR-S has the unique property of causing lower interfacial tensions between brine and Soltrol with increasing salt concentrations in the brine. The effect of increasing brine concentrations on the surface tension of water containing 0.1% and 0.5% Triton GR-S is illustrated in Table IV.

TABLE IV Percent Percent y, dyneS/cm. Triton Gli-5 NaCl 0. 1 0. 1 0. S6 0. 1 0. 3 0. 26 0. 1 1. 0 0. 07 0. 1 2. 5 0. 025 0. 5 0. 1 0. U6 l). 5 l). 25 0.35 0. 5 1. 0 0. 06 0. 5 2. 5 0. 025

The cationic surfactants can also be used to reduce the interfacial tension to the desired range, but in general are not as desirable for this purpose as the nonionic or anionic surfnctants because the cationic surfactants tend to be adsorbed on the surface of the formation rock.

Suitable cationic surfactants for causing the desired low interfacial tension are DH 1080 and Hyamine 2389 manufactured by Rohm and Haas. These surfactants will reduce the oil-water interfacial tension to 0.4 and 0.5 dyne/cm., respectively, at 0.5% concentrations. Cationc surfactants are usually quaternary ammonium chloride salts with one or two long alkyl-aryl groups on the nitrogen atom to impart the oil-water interfacial activity. For example, Hyamine 2389 is a mixture of alkyl tolyl methyl trimethyl ammonium chloride with the alkyl group ranging from (29H19 to Cll-lal and an average molecular EXAMPLE 1 A cylindrical Berea sandstone core, 4.51 centimeters long and having a cross sectional area of 5.06 square ccntimeters, was saturated with a brine solution containing 2l/z% sodium chloride. Following'the saturation with the brine solution, the core was flooded with Soltrol until no further brine was driven from the core. Following the Sotrol flood, the core was then flooded with 21/2% brine ata rate below a ratio of 5 until no further oil was recovered, thereby leaving residual oil in the core. An aqueous surfactant solution containing 0.25% Triton GR-S and 2.5% sodium chloride was then forced through the core. The surfactant solution had an interfacial tension with the Soltrol of 0.07 dyne/cm. A pressure of 0.40 pound per square inch was applied to the surfactant solution at the inlet end of the core resulting in a of 38.2. The results are presented in the following Table i ln Tables V and VI, the terms SO, Sor, and SW refer to the volume of oil, residual oil, and water, respectively, in the core at the end of the step. to the volume of the liquid in cubic centimeters and percentVp refers to the volume of the liquid in terms of the pore volume of the core.

TABLE V Berea core N 0. B-21 Oil Production Core Sat urnt ion Process Completed So Sw Percent C'C. Vp

Cc. Percent Ge. Percent Vp VP Saturated with 2.5% NaCl 5. 3 100 Soltrol Flood.- 2. 94 55. 5 2. 3G 44. 5 Brine Flood. 0. 98 18. 5 l. 90 37 3. 34 03 .Flood of 0.25%

GR-5 in 2.5%

NaCl. Il. 99 38 0. 00 O. 00 5. 3 100 1 The oil production of L99 ce. indicates substantially connut-te retrieval of oil from the core, Within the accuracy of the measurements.

EXAMPLE 2 A Beren sandstone core, one inch in diameter and 2.32 centimeters long, was saturated with a brine solution containing 21/172: sodium chloride. The core was then flooded with N. Ward Estes Crude Oil after which it was flooded with brine at a i The term cc. refers for the test was 37.5. The results of the flood are presented in Table VI.

TABLE VI Oil Production Coro Satlxratlons Process Completed So Sw Percent Ce. VP

Cc. Percent Cc. Percent VP VP Plug from Long Berea Coro Saturated with 1.5% Nu(."l 2.59 100.00 Crude Oil l `lootl 1. 67 64.5 0. 92 35. 5 Brine Floofl 0.80 30. 9 0. 87 33.6 1. 72 66.4 Flood of l l'ore Vellum of Solar 25 Followed hy Brille 1 0. 52 20. 0 0. 35 13. 5 2. 24 86. 5

l 60% of Sor.

Laboratory results on the flooding of cores are of little' value for application to the flooding of oil fields unless a proper correction is made for the high pressure gradients that are ordinarily employed in the laboratory work. Comparable pressure gradients cannot be obtained in the flooding operations as they have been performed in oil fields. In addition to reducing the interfacial tension between the oil and flood water to the desired low range below 0.2 dyne/ centimeter, it is essential to control the flood pattern to obtain a linear drive to obtain ratios high enough to cause substantial production of residual oil. Conditions existing in oil fields having ordinary well spacing, regardless of whether the flood is the usual five spot flood pattern or a line drive pattern in which the injection of the flood water is at a number of wells in a line, require flood rates or injection pressures higher th-an can practicably be obtained. The chart in the Transactions of the Alb/LE., Vol. 103, 1933, page 230, shows that a major portion of the area ooded in a five spot pattern is subjected to a pressure gradient approximately onefourth of the average pressure gradient between the injection and production Wells and less than of the pressure gradient occurring in the distance from the injection well in which the first 20% of the pressure drop occurs. ln order to subject the entire flooded area to a pressure gradient adequate to produce the critical L'r ratio, the pressure gradient between injection and production wells must be approximately four times that required to produce the critical Hence, reduction of the interfacial tension between the flood water and the oil in the formation is not alone surficient to eliminate the necessity of the excessive flood rates mentioned in the Oil and Gas Journal article, supra.

Itis possible to have a substantially uniform pressure gradient through the ooded formation and avoid the very high pressure gradient over a portion of the formation that would be required to exceed the critical ratio in processes of the prior art by employing a true linear drive. The term linear drive is herein used in distinction to the ordinary line drive process to designate a process in which the areas of the for-mation exposed t0 open passages from the injection well and the production well are of the same order of magnitude as the area in the 9 formation swept by the flood water perpendicular to the d-irection of flow of the flood water. The area of the passages should exceed about 10% of the area of the formation perpendicular to the direction of flow. In the ordinary line drive process the area of the passages is equal to the exposed area of the vborehole wall ofthe well which is only a very small fraction, less than about 0.5%, depending upon the well spacing, of the area of the formation perpendicular to the direction of flow.

Several' methods are available for obtaining the desired linear flow pattern. Referring to FIGURE 2 of the drawings, an injection well, indicated generally by reference numeral 10, is drilled through a producing formation 12 from which oil is to be recovered by the water flooding process of this invention. For purposes of illustration, casing 14 is set in well 10 completely through the oilbearing zone 12 and is cemented in place in accordance with conventional practice. -A production well 16 spaced from the injection well 10 a distance determined by the usual considerations in oil field development is drilled into the oil-bearing formation 12 and casing 18 is set in accordance with conventional practice.

A horizontal ring is cut through the casing 14 in the lower portion of the oil-bearing formation 12 and a large horizontal fracture 20 is made to extend from the well 10 in the lower portion of the oil-bearing formation 12. Fracture 20 can be made by suitable modification of the process described in United States Patent No. 2,699,212 to cut a horizontal notch in the formation at the location of the section milled 'from casing 14 and thereafter pumping a suitable fracturing fluid into the formation at a pressure high enough to cause a fracture. The pumping-of the -fracturing fluid is continued for a period and at a rate adequate to extend the fracture to the vicinity of well 16. The fracture 20 is propped open by a propping agent pumped into the fracture either during or subsequent to the formation of the fracture.

A section ismilled from the casing 18 of well 16 in the upper portion of the oil-bearing formation 12 in the manner described for well 10. A large horizontal fracture 22 is formed in the upper portion of the oil-bearing formation extending from the cut out section of casing 18 of well 16 in a 4manner similar to that described for fracture 20. Fracture 22, like fracture 20, is propped open with a suitable propping agent to form a fracture of high flow capacity extending from well 16.

Following the formation of fracture 20 a packer 24 is set in well 10 above the level of the fracture 20 and tubing 26 run through the packer. Similarly, a packer 28 is set in well 16 above fracture 22 and tubing 30 run through packer 28. Flood water treated with a surfactant 'to give an interfacial tension between the oil in the formation and the flood water less than 0.5 dyne/centimcter and preferably less thanv 0.2 dyne/centimeter is delivered through tubing 26 and fracture 20 into the formation 12 at a pressure adapted to cause a where L is the vertical distance between fractures 20 and 22 in feet, preferably in excess of 20. Oil flooded from the formation 12 is delivered into the fracture 22, through that fracture into well 16, and the oil can then be lifted to the surface either by the pressure exerted on the flood water or by the provision of a suitable pump in well 16.

ln the embodiment of the invention illustrated in FIG- URE 3 of the drawings, a plurality of injection wells 32a and B2b are interconnected in the oil-bearing formation by vertical fractures 34 and 36. Spaced from the injection wells 32a and 32h are production wells 38a, 3815, and 38e. interconnecting vertical fractures 40, 42, and 44 through the oil-bearing formation penetrated by the injection and production wellsrconnect the production weils in a line generally parallel to the fractures 34 and 36 connec-ting the injection wells. The vertical fractures connecting the injection wells and those connecting the production wells can be made by the process described in United States Patent No. 2,699,212.

Oil is produced from the formation by pumping an aqueous surfactant solution into injection wells 32a and B2b. The surfactant solution ows outwardly through vertical fractures 34 and 36 and from those fractures into the exposed face of the formation. The rate of pumping the aqueous surfactant solution is adjusted -to maintain the ratio of where L is the distance between the interconnecting fractures joining the injection wells 32a and 32b and the interconnecting fractures joining the production wells 38a, 38b, and 38C, above the critical value and preferably above 20. Residual oil in the formation is driven by the surfactant flood into the fractures 40, 42, and 44 and through the production wells 38a, 38h, and 38C through which the oil is lifted to the surface.

The wells illustrated in FIGURE 3 of the drawings are arranged in the usual pattern which results in a fivespot flood pattern in secondary recovery operations. A comparison of the linear drive described with reference to FIGURE 3 and a conventional five-spot dood pattern illustrates the advantages of the applicants invention.

Assuming a well spacing of ten acres per five-spot pattern, the wells in each row will be 666 feet apart. The distance between adjacent rows is one-half the well spacing or 333 feet which is also the average distance between the fractures connecting the injection wells and the fractures connecting the production wells in FIGURE 3. lf a tive-spot flood pattern were used, water injected in well 32a would flow to well 38a or well 38b, which are 467 feet from the well 32a. Assuming flooding a formation with a pore size distribution similar to Berea sandstone with an aqueous surfactant solution which has an interfacial tension with the oil in the formation of 0.1 dyne/centimeter at a maximum pressure of 800 pounds per square inch, approximately 50% of the residual oil can be recovered in the linear drive process while no residual oil can be recovered in the five-spot pattern, as illustrated by the following Table VII.

1. A water flooding process for the recovery of residual oil from an underground oil-bearing formation having an injection well and a production Well spaced from the injection well penetrating the formation compn'sing forming a first passage extending into the oilbearing formation from the injection Well, forming a second passage extending into the oil-bearing formation from the production well, said first and second passages being substantially parallel, injecting an aqueous dispersion of a surfactant from the injection well into the formation at a pressure whereby the pressure differential in pounds per square inch between the first and second passages per foot of distance between the passages divided by the interfacial tension in dynes per centimeter between the oil in the formation and the aqueous dispersion exceeds l l about displacing said dispersion through thc formation to drive oil through the formation to thc production well, the area of the formation exposed to each of said rst and second passages being at least 1/ 10 of the area swept by the aqueous dispersion measured perpendicular to the direction of ow of the aqueous dispersion, and producing oil through the production well.

2. A process as set forth in claim 1 in which the interfacial tension between the oil in the formation and the aqueous dispersion of a surfactant is less than .2 dyne/centimeter.

3. A process as set forth in claim 1 in which the ratio of the pressure differential in pounds per square inch between the first and second passages per foot of distance between the passages divided by the interfacial tension in dynes per centimeter between the oil in the formation and the aqueous dispersion exceeds about 20.

4. A process as -set forth in claim 1 in 'which the aqueous surfactant dispersioncontains at least about 2% sodium chloride and the surfactant is asodium dioctyl suifosuccinate.

' 5. A process as set forth in claim 1 in which the first passage is a substantially horizontal fracture at one level in the oil-bearing-formation and the second passage is a substantially horizontal fracture at a different level in the oil-bearing formation than the first fracture.

6. A process as set forth in claim 1 in which the first passage is a substantially vertical fracture extending from the injection well in the oil-bearing formation and the second passage is a substantially vertical fracture extending from the production well in the oil-bearing formation. A

7. A- process as set forth in claim 1 in which the aqueous dispersion is an aqueous dispersion of a nonionic surfactant and contains sodium hydroxide in concentrations up to about 5%.

8. A water flooding process for the recovery of residual oil from an underground oil-bearing formation penetrated by a series of injection wells in a substantially straight line and a series of production wells spaced from the injection wclls in a substantially straight line parallel to a line joining the injection wells comprising forming a series of vertical fractures connecting the injection wells to form a first passage for the injection of flood water, forming interconnecting vertical fractures from the production wells in the oil-bearing formation to form a second passage substantially parallel to the first passage, injecting an aqueous dispersion of a surfactant into the injection wells whereby the aqueous dispersion flows into the first passage into the formation to drive oil through the formation concurrently with the aqueous dispersion toward the second passage, displacing the dispersion t through the formation to the second passage under a pressure such that the pressure differential in pounds per square inch between the first and second passages per 'foot of distance between the passages divided by the interfacial tension in dynes per centimeter between the oil in the formation and the. aqueous dispersion exceeds about 5, said aqueous dispersion having an interfacial tension with the oil less than about 0.2 dyne/centimeter, each of said first and second passages exposing an area of the formation at least 1/10 the area swept by the aqueous dispersionmeasured perpendicular tothe direction of flow of the aqueous dispersion, and producing oil through the production wells.

References Cited by the Examiner UNITED STATES PATENTS 1,651,311 11/27 Atkinson 166-9 2,792,894 5/57 Graham et al 166-9 X 2,862,556 12/58 Tek 166--10 2,952,319 9/60 Popbarn 166-35 2,966,346 12/60 Huitt et al. 1,66--421 X 3,006,411 10/61 Holbrook 166-9 GTHER REFERENCES Moore, T. F., and Blum, H, A.: Wettabilityin Surface- Active Agent Water Flooding, Oil and Gas Journal, Dec. 8, 1952, pp. 108, 109, 111.

CHARLES E. oCoNNELL, Primi-y swimmer.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,199,586 August 10, 1965 James H. Henderson et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

for "5:5" read 5.5

Column 4, line 14,

line 36 for Q i "percent" read cannot column S, line 74, for "aqeous" read aqueous column 8, lines 5S to 57, for the ratio reading .e 1E LY read LY column 10, line 43, for "can be" read is Signed and sealed this 22nd day of February 1966.

EAL)

test:

NEST W. SWIDER EDWARD I. BRENNER estng Officer Commissioner of Patents 

1. A WATER FLOODING PROCESS FOR THE RECOVERY OF RESIDUAL OIL FROM AN UNDERGROUND OIL-BEARING FORMATION HAVING AN INJECTION WELL AND A PRODUCTION WELL SPACED FROM THE INJECTION WELL PENETRATING THE FORMATION COMPRISING FORMING A FIRST PASSAGE EXTENDING INTO THE OILBEARING FORMATION FROM THE INJECTION WELL, FORMING A SECOND PASSAGE EXTENDING INTO THE OIL-BEARING FORMATION FROM THE PRODUCTION WELL, SAID FIRST AND SECOND PASSAGES BEING SUBSTANTIALLY PARALLEL, INJECTING AN AQUEOUS DISPERSION OF A SURFACTANT FROM THE INJECTION WELL INTO THE FORMATION AT A PRESSURE WHEREBY THE PRESSURE DIFFERENTIAL IN POUNDS PER SQUARE INCH BETWEEN THE FIRST AND SECOND PASSAGES PER FOOT OF DISTANCE BETWEEN THE PASSAGES DIVIDED BY THE INTERFACIAL TENSION IN DYNES PER CENTIMETER BETWEEN THE OIL IN THE FORMATION AND THE AQUEOUS DISPERSION EXCEEDS ABOUT 5 DISPLACING SAID DISPERSION THROUGH THE FORMATION TO DRIVE OIL THROUGH THE FORMATION TO THE PRODUCTION WELL, THE AREA OF THE FORMATION EXPOSED TO EACH OF SAID FIRST AND SECOND PASSAGES BEING AT LEAST 1/10 OF THE AREA SWEPT BY THE AQUEOUS DISPERSION MEASURED PERPENDICULAR TO THE DIRECTION OF FLOW OF THE AQUEOUS DISPERSION, AND PRODUCING OIL THROUGH THE PRODUCTION WELL. 